toString methods

.toISOString() has no modifiers and will produce a standard ISO 8601 time-stamp string, ie. 1972-07-01T00:00:00.000Z

Pattern formatting

.format("YYYY'-W'ww'-'E") // 2013-W46-3

Date and time formats are specified by date and time pattern strings. Within date and time pattern strings, all unquoted ASCII letters [A-Za-z] are reserved as pattern letters representing calendar fields.
astrodate supports the date and time formatting algorithm and pattern letters defined by UTS#35 Unicode Locale Data Markup Language (LDML)

Any characters in the pattern that are not in the ranges of ['a'..'z'] and ['A'..'Z'] will be treated as quoted text.
For instance, characters like ':', '.', ' ', '#' and '@' will appear in the resulting time text even they are not embraced within single quotes.

A pattern containing any invalid pattern letter will result in a thrown exception during formatting.